Spinal Cord Anatomy and Ascending and Descending Pathways Flashcards
What do somatosensory afferents and motor efferents to skeletal muscle travel by?
Spinal cord
Spinal cord function
Receives 1o afferent fibres from peripheral receptors
Sends motor axons to skeletal muscle
Communications between brain and periphery
Preganglionic neurons of SYM and some of PSYM
How many spinal nerves does the spinal cord produce?
31
What are the enlargements associated with?
Cervical = upper limb Lumbar = lower limb
What occurs at each segment?
Rootlets from dorsal and ventral produce ant and post rootlets
Passing through subarachnoid space until reach vertebral formina
Post root is enlarge by dorsal root ganglion
Fuse = mixed spinal nerve= ant and post rami
What is the spinal cord continuous with?
Medulla below foramen magnum
Tapered cone shape spinal cord terminates as?
Conus medularis
What does the conus medularis continue as?
Filum terminale (thin CT) Anchored to dorsum of coccyx
Where does the spinal cord end?
L1 (L2 at birth)
Where is the dural spinal cord and what does it include?
Below L1
Dorsal and ventral roots of L2 and lower nerves of filum terminale
What is the collection of roots of the filum terminale called?
Cauda equina
Where does the dural sac end?
S2
Dorsal and ventral roots pass out of the sack, remain in dura and travel in spinal canal now in CSF of subarachnoid space
How are the spinal cord meninges continuous with the cranial meninges?
Foramen magnum
What is the spinal cord suspended by?
Denticulate ligament
How is the denticulate ligament formed?
From pial and arachnoid tissue
Dorsal and ventral roots in IVC and dura and arachnoid mater merge with
CT around the nerve
Where is the white mater located on the spinal cord?
Outside
Where is the grey mater located on the spinal cord?
Inner H
What does the white mater consist of?
Longitudinal axons
Glial cells
Blood vessels
What does the grey mater consist of?
Neuronal soma Cell processes Synapses Glia Blood vessels
Where does the small central canal running the length of the spinal cord open and close?
Rostral - opens into 4th ventricle
Caudal - blind ending - medulla?
What occurs if there is damage to the white mater?
No more communication below that level
What occurs if there is damage to the grey mater?
Damage/paralysis in band that is damdaged
Where is grey mater greatest?
Cervical and lumbar enlargements
Where is white mater greatest?
Cervical levels and less at caudal levels
Where is the lateral horn/intermediolateral cell group?
And what does it contain?
T1-L2
Preganglionic SYM neurons
SYM outflow
Where is the PSYM outflow?
Above and below SYM outflow
How are rexed laminae defined?
Cell size
Shape
Density
Lamina I
Lamina marginalis
large diameter afferents synapse here
Lamina II
Substantia gelatinosa
Pain fibres here
Lamina III
Part of substantia genlatinosa and nucleus proprius
Afferents
Lamina IV
Part of nucleus proprius
dendrites of tract cells
Lamina V and VI
Base of dorsal horn Proprioceptive afferents Motor and sensory Movement (important in) Tract cells = give rise to spinothalamic tract
Lamina VII
Intermediate horn
Clarke’s column (T1-L2)
Proprioceptive fibres synapse
Intermediolateral column (T1-L2) = SYM preganglionic neurons
Lamina VIII
Proprioceptive interneurons
Lamina IX
Alpha and gamma motor neurons
Lamina X
Dorsal and ventral grey commisures
Where is the tract of Lissauer?
Overlying lamina I
Thin layer of white matter
Afferents (pain + temp) enter cord divide into ascending and descending branches before entering grey matter
Arterial supply of spinal cord
Ant and 2 post longitudinal aa. = originate from vertebral aa. (run length of cord)
Segemental aa. - from vertebral, deep, cervical, intercostal and lumbar aa.
Radicular aa. - travel along dorsal and ventral roots
What is the great anterior segmental medullary artery?
Large radial a T9-11
Supplies much of lower spinal cord
What does the anterior spinal artery supply?
2/3rd of the spinal cord (cross section)
What do longitudinal veins drain to?
Cerebellar veins and cranial sinuses
What do segmental veins drain to?
Local vertebral plexuses then thoracic/ abdominal/ intercostal veins
What is the epidural space occupied by?
Adipose tissue between bone and dura
Used in epidural anaesthesia
Dorsal column (ascending tract)
Cuneate nucleus and gracile nucleus
Fine touch and conscious proprioception and vibration sense
Cross in medulla (Crossing of fibres – decusation)
Arm =CF
Leg=GF, graceful
Synapse in medulla but also in nucleus granculus=medial and nucleus cuneatus –lateral
What is proprioception?
sense of the relative position of one’s own parts of the body and strength of effort being employed in movement
Proprioception in lower limb
Some via the DC system. Some ascends in the DC to thoracic/upper lumbar regions
Synapses in Clarke’s column,
Projects to the medulla in the dorsal spinocerebellar tract. Then rejoins medial lemniscal system to reach thalamus and cortex.
Other name for Clarke’s column
Nucleus dorsalis
Spinothalamic tract (as. tract)
Pain, temp and deep pressure
Fibres cross segmentally
Tracts cells in lamina V-VI give rise to?
Spinothalamic tract
Primary somatosensory cortex and sensory cortical homunculus
Somatotopic organisation of neurons = mapped out
Sensory fibres crossed midline
Left side of body = right cortex
Corticospinal tract (descending tract)
Control of precision and speed of skilled movements
Ridges (pyramids) on ant surface of medulla = pyramidal tract
85% fibres cross at caudal medulla - decussation of pyramids
Crossed fibres from Lat CST
Uncrossed = ventral CST - cross segmentally
CST fibres travel in?
Post limb of internal capsule
Rubrospinal tract
Excitory control of tone of limb flexor muscles
Originate in red nucleus of midbrain and decussate here
In lat column in SC, lat to CST
Ends in upper C spinal cord
Tectospinal tract
Small tract, input from C
O in sup colliculus (tectum)
Mediate reflex movement due to visual stimuli
Lateral Vestibulospinal Tract
Excitatory input to “antigravity” extensor muscles.
O in the ipsilateral vestibular nuclei of pons and medulla (these in turn receive input from vestibular apparatus and cerebellum).
Fibres do not cross
Reticulospinal Tract
Reticular formation forms the central core of the brainstem - IMPORTANT
Many nuclei and receives input from virtually all parts of the CNS.
Influencing of voluntary movement.
O in areas of the reticular formation in pons and medulla.
Fibres originating in pons facilitate extensor movements and inhibit flexor movements, while those originating in the medulla do the opposite. Also, because some fibres extend to many spinal levels it is thought they may help coordinate movement involving upper and lower limbs.
Motor system outside of pyramidal tract is the
Extrapyramidal system
Brown – sequard syndrome
Hemisection of the spinal cord- numb to fine touch, loose pain and temp fibres on opposite side